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A year and a half after the Mullen Fire, plants and wildlife are making a comeback

A plume of smoke drifts above a prairie landscape.
U.S. Forest Service

In late 2020, the Mullen Fire scorched 176,878 acres of land in the Snowy Range 28 miles west of Laramie. The Wyoming Game and Fish Department (WGFD) has been closely monitoring the area and the wildlife that call it home since then.

"I think many of us understood that we were probably long overdue for a catastrophic fire event due to the fuel loading that was occurring in that forest because of the dead lodgepole pine caused by mountain pine beetle epidemics," said WGFD terrestrial habitat biologist Ryan Amundson. "It wasn't a matter of if, it was a matter of when."

The winter and spring directly following the fire were drier than normal, followed by an unusually hot start to summer in 2021, so plants struggled to regrow. But monsoonal moisture later in the summer helped turn that around. And according to Amundson, the dry start may have actually been beneficial.

"If we'd have had very high snowpack levels and there'd been a large runoff event, we likely would have seen more soil movement and more soil erosion and we probably would have seen a lot more siltation sedimentation into the stream systems," he said. "And because we did not have the large runoff events and it was a much slower melt, we didn't see nearly as much soil movement, which is a very positive thing."

Amundson said the fire also cleared some of the lodgepole pine forest and allowed the aspens to regrow in areas they'd previously been pushed out of. It's also giving wildlife more opportunities to spread out and eat the nutritious young plants.

"The good thing about a fire of that size and scale is that it does spread herbivory out throughout the forest. So hopefully, animals aren't having adverse or negative impacts to those plant communities as they're trying to re-establish," said Amundson.

He said the loss of lodgepole pines will also likely benefit the local Douglas Creek bighorn sheep herd because sheep don't like to travel through heavy canopies of coniferous forest.

The WGFD was already studying the herd's movements before the Mullen Fire with GPS collars. The fire created a natural experiment for the department to observe how the sheep respond to the changes in the burn scar. The collars gather data for about three years and the department will be deploying more soon.

"We anticipate that bighorn sheep are going to make some larger movements and find other suitable habitats within the southern portion of the Snowy Range," said Amundson.

But in order for the burn scar to recover suitably now, Amundson is hoping for a near to above normal spring in terms of precipitation.

"Since the stream systems are buffered so well now from one year of regrowth, I think we're in a really good position for that and we could handle larger precipitation events," he said. "And it's going to really take that to get native perennial grass and forb and shrub recovery this coming year."

Amundson added that the area is also highly vulnerable to invasive cheatgrass right now, so the department is treating certain areas with a selective herbicide to minimize its ability to take hold. They've already treated 10,334 acres and may treat up to 5,000 acres this coming summer.

"The first two and three years postfire is definitely the most critical period of time and we're watching it like a hawk to make sure that things are headed in the right direction," he said.

Ivy started as a science news intern in the summer of 2019 and has been hooked on broadcast since. She was supported by the Wyoming EPSCoR Summer Science Journalism Internship program. In the spring of 2020, she virtually graduated from the University of Wyoming with a B.S. in biology with minors of journalism and business. She continues to spread her love of science, wildlife, and the outdoors with her stories. When she’s not writing for WPR, she enjoys baking, reading, playing with her dog, and caring for her many plants.
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